204 THE LOWER FUNGI— PHYCOMYCETES 



amphigynous antheridia is pictured. Such cases have not yet 

 been explained. The latter case would appear to be inexplicable 

 in the light of Murphy's account, and the question is raised 

 whether the amphigynous antheridium has that position because 

 the oogonium has grown through it or for some other reason 

 such as the coiling of the antheridium around the base of the 

 oogonium (Cooper, 1928; Cooper & Porter, 1928). No cyto- 

 logical evidence has been advanced to refute the observations of 

 Murphy, who in the study of serial sections, found the base of 

 the oogonium within the antheridium. 



A satisfactory basis for separation of species within the 

 genus Phytophthora has not yet been found. Many species have 

 been described, but the identification of an unknown form is often 

 difficult if not actually impossible. A number of specific names 

 at present applied will doubtless in time be place in synonymy. 

 Tangible morphological characters are few and variable, while 

 separations based on host relationships and cultural characters 

 have proved inadequate. A thorough taxonomic revision of the 

 genus and its close relatives is now imperative. 



Considerable taxonomic work has been done on the genus by 

 Rosenbaum (1915; 1917) andLeonian (1925). The former author 

 presents a key separating eleven species. In his studies he uses 

 biometrical methods, and bases his spore and sporangia! measure- 

 ments on the examination of hundreds of individuals. His 

 method, while perhaps sound, is extremely laborious in applica- 

 tion. Leonian presents a key separating eighteen species on cul- 

 tural characters. The presence or absence of sporangia or oogonia 

 on specified media afford the basis for separation. Leonian 

 (1927) also states that remarkable modifications in the mor- 

 phology of the sporangium take place when a given species is 

 grown on various hosts. He concludes that material taken 

 directly from the host for identification is less desirable than 

 that developed under controlled cultural conditions in the 

 laboratory. More recently Leonian and Geer (1929) have made 

 a comparative study of the size of sporangia in many species, 

 and conclude that many specific names now used must be thrown 

 into synonymy. Workers in general have stressed host rela- 

 tionships in delimiting species, and in a number of cases new 

 species have been erected, chiefly because new hosts were involved. 



In no published paper have all the described species been 

 discussed together. At present thirty or more species exist in 



